The invention described herein relates to derivatives of (R) and (S)-carnitine, and particularly nitriloxy derivatives which are useful as intermediate synthesis products and as therapeutic agents.
Organ ischaemia is caused by an imbalance between the oxygen requirements of the tissue and oxygen availability from the bloodstream. In the particular case of cardiac ischaemia, this If manifests with typical symptoms, known as angina pectoris. The causes are multiple and, among them, we should mention the reduced ability of the coronary circulation to supply oxygen, owing, for example, to the presence of atheromatous plaques. One possible consequence of the ischaemia is myocardial infarction.
Myocardial ischaemia may also be asymptomatic and detectable only by means of clinical and instrumental examinations.
The therapy currently available is based mainly on the administration of coronary dilating drugs, which, on account of the specific needs of symptomatological treatment, have to have as rapid an action as possible. Calcium antagonists, xcex2-adrenergic antagonists and antiaggregant agents should also be mentioned.
Among the drugs still most commonly used today, we should mention the organic nitrates, which by releasing NO at the action site exert a local vasodilatory action.
Amyl nitrite is used by inhalation in cases of angina attack. Nitroglycerine and organic nitrates of higher molecular weight are also used for the prevention of such attacks. Nitroderivatives are associated with a series of important side effects. The most common of these is headache, which may even be very severe. More serious is the fact that these drugs give rise to tolerance and their withdrawal causes a rebound effect. Nitroglycerine is also administered using transdermal release systems, which, however well designed they may be, present problems in their own right, such as those relating to permanence at the application site, controlled delivery of the drug and patient compliance.
Calcium antagonists present the problem of excessive vasodilatation, with consequent dizziness, hypotension, headache, and nausea, and it is by no means easy to establish the appropriate therapeutic regimen.
xcex2-antagonists have effects on cardiac haemodynamics.
For a more detailed discussion of these aspects, the reader is referred to Goodman and Gilman""s The Pharmacological Basis of Therapeuticsxe2x80x949th edition, chapter 32.
To date, no single drug therapy is available for the treatment of ischaemic states, particularly angina pectoris, which possesses the desired characteristics in terms of patient compliance, safety of use, lack of side effects and immediacy of action. In particular, no ester of nitric acid is as yet available which combines the characteristics of immediacy of action and a lack of the side effects typical of this class of drugs.
Patent application WO98/56759 describes pentaerythrite derivatives of general formula (O2NOCH2)mC(CH2OH)n(CH2COR1)o(COR1)p. The multiple meanings of R1 include nitriloxy derivatives of carnitine, in particular nitriloxy-carnitine chloride, its inner salt and ester with (1-alkoxy-carbonylmethyl-2-trialkylammonium)ethanol. An ester of racemic nitriloxy-carnitine with (1-alkoxycarbonylmethyl-2-trialkyl-ammonium) ethyl alcohol is also envisaged, provided on mixtures containing equimolar amounts of (R) and (S) isomers. The anti-angina activity of these compounds is mentioned in the description. Nitriloxy-carnitine is also prepared as an intermediate. The examples of the compounds are provided on the racemic mixtures. The only example of a preparation, example 17, which uses L-carnitine, envisages reaction with the chloride of 3-nitriloxy-2,2-bis(nitriloxymethyl)propionic acid. The resulting compound (not identified either in physico-chemical or in structural terms) is not included in the claims and is not mentioned in relation to its presumed pharmacological activity. The patent application cited does not provide a general scheme for preparation of the compounds, and thus the compounds effectively described are to be found in the preparation examples. No pharmacological activity data are provided.
The action of L-carnitine in the treatment of heart failure is known (U.S. Pat. No. 3,830,931).
Also known is the fact that acetyl L-carnitine enhances the oxidation of glucose and prevents the accumulation of lactate in the concomitant acidosis (Lopaschuk, G. in Carnitine Today-C. De Simone and G. Famularo ed. ) Lands Bioscience 1997).
Alkanoyl derivatives of L-carnitine are known for different uses in human or animal therapy.
It has now surprisingly been found that enantiomerically enriched nitriloxy derivatives of (R) or (S)-carnitine are endowed with favourable and advantageous pharmacological activities, particularly as therapeutic agents for organ ischaemias, and even more particularly for the treatment of angina pectoris.
Nitriloxy derivatives of (R) and (S)-carnitine are also useful intermediates for synthesis for the production of chiral 3-4 carbon atom synthons having the (R) or (S) configuration, such as for example 3-hydroxy-xcex3-butyrolactone, 1,2,4-butantriole, 3-hydroxytetrahydrofurane, 3-hydroxypyrrolidine, 2,3-dihydroxypropylamine, to be used in the industrial synthesis of enantiomerically pure drugs. However, (R) and (S)-carnitine are not actually available at low cost, therefore a process convenient and applicable on a large scale, allowing the stereospecific conversion of (S)-carnitine into (R)-carnitine or vice-versa will be economically advantageous and useful.
It has now surprisingly been found that enantiomerically enriched nitriloxy derivatives of (S)-carnitine, according to the present invention, are suitable intermediates for the production of (R)-carnitine its derivatives, and vice-versa.
The subject of the invention described herein are carnitine derivatives of general formula (I) in optically active form of absolute configuration (R) or (S) 
where
Y is an OR or NR1R2 group with
R equal to hydrogen, C1-C10 alkyl or alkyl substituted with C6-C10 aryl, said aryl optionally carrying one or more C1-C4 alkyls;
R1 and R2, which may be the same or different, are hydrogen, C1-C10 alkyl or alkyl substituted with C6-C10 aryl, said aryl optionally carrying one or more C1-C4 alkyls; or, taken together, form a 5-7 atom heterocyclic ring with the nitrogen atom;
or Y is the residue of an esterified polyalcohol with at least one nitric acid equivalent;
Xxe2x88x92 is the anion of a pharmaceutically acceptable organic or inorganic acid,
or, if Y is an OH group, the formula (I) product may exist in the form of an inner salt, i.e. with structure (II) 
and their enantiomerically enriched mixtures.
Examples of C1-C10 alkyls are methyl, ethyl propyl, butyl, pentyl, hexyl, octyl, nonyl, decyl and all their possible isomers.
Examples of substituted alkyls are benzyl and phenylethyl.
Examples of substituted aryls are tolyl, xylyl and its isomers.
Examples of polyalcohols are glyceryl mono- or dinitrate, isosorbide mononitrate, erythrityl di- o trinitrate, pentaerythrityl mono-, di- or trinitrate.
Examples of anions of organic or inorganic acids are NO3xe2x88x92, Clxe2x88x92, Brxe2x88x92, Ixe2x88x92, HSO4xe2x88x92, (SO42xe2x88x92)0.5, H2PO4xe2x88x92, (HPO42xe2x88x92)0.5, (PO43xe2x88x92)0.33, a residue of a hydroxy acid, a residue of a bicarboxylic acid, OSO2Zxe2x88x92, OCOZxe2x88x92 or OCOHxe2x88x92 with Z equal to C1-C10 alkyl, substituted alkyl, such as, for example, trihalomethyl or benzyl, aryl, such as, for example, phenyl, tolyl, halophenyl or alkoxyphenyl. What is meant by halogen is fluorine, chlorine, bromine and iodine. Preferred examples of anions of organic and inorganic acids are those derived from pharmaceutically acceptable acids, among which, in addition to those exemplified above, we would mention particularly mandelate, orotate, acid aspartate, acid citrate, fumarate and acid fumarate, maleate and acid maleate, mucate, malate and acid malate, glucose phosphate, tartrate and acid tartrate, succinate, acid succinate, oxalate.
Examples of a heterocyclic ring with 5-7 nitrogen atoms are tetrahydropyrrhol, piperidine, piperazine, morpholine, alkyl-morpholine and azepine.
Compounds whose absolute configuration is (R) are preferred.
Additionally preferred are compounds whose absolute configuration is (R) and in which Xxe2x88x92 is an anion of a pharmaceutically acceptable acid, namely the compound of formula (I) in the form enantiomerically enriched of absolute configuration (R)
A further subject of the invention described herein is the process for the preparation of formula (I) or (II) compounds, using procedures which are in themselves known, starting from formula (III) compounds with known nitrating agents, such as, for example, concentrated nitric acid, a nitric acid/sulphuric acid mixture, a nitric acid/acetic anhydride mixture, etc., when T is a hydroxy group or when T is a good leaving group; or by means of treatment with alkaline nitrates, earth-alkaline nitrates, silver nitrate, ammonium nitrate or tetra-alkylammonium nitrate, when T is a good leaving group, such as, for example, an OSO2Z group, where Z is as defined above.
The process is illustrated in the following scheme: 
where T is a hydroxy group or T is a leaving group, X1xe2x88x92, equal to or different from Xxe2x88x92, being included in the meanings illustrated above.
The Xxe2x88x92 group, as required and using techniques in themselves known, such as the use of ion-exchange resins or by means of electrodialysis, can be varied in the context of the possibilities listed above, subsequent to treatment with the nitrating system.
Formula (III) products are optically active and, according to the nitrating system used, formula (I) products can be obtained, with the same absolute configuration as the formula (III) products or with the opposite absolute configuration, and, to be precise, retention of absolute configuration occurs when the nitrating agent used in the course of the reaction does not involve the formation of a bond with the asymmetric carbon atom, while inversion of configuration is observed when using nitrating agents whose mechanism of action involves an SN2 nucleophilic substitution reaction with substitution of the T group.
A further subject of the invention described herein is the use of formula (I) compounds, and particularly of derivatives with Y equal to an OH group and Xxe2x88x92 equal to NO3xe2x88x92, Clxe2x88x92, OSO2Zxe2x88x92 or OCOZxe2x88x92 with Z equal to C1-C10 alkyl, or of the formula (II) compound, preferably in the optically active form of absolute configuration (R) and in the case of enantiomerically enriched mixtures, said mixtures preferably comprising an amount of the enantiomer (R) higher than 95%, as pharmaceutically active anti-angina ingredients in solid and liquid pharmaceutical compositions for oral administration, parenteral administration, transdermal use or sublingual use in the treatment of ischaemic heart disease.
Said compositions include a pharmaceutically effective dose of the active ingredient, optionally in mixtures with pharmaceutically acceptable vehicles or excipients. The invention described herein also relates to a therapeutic method for the treatment of angina pectoris and of various ischaemic forms, comprising the administration of said compositions in amounts corresponding to 1-200 mg of active ingredient per day orally, of 0.1-10 mg of active ingredient per day parenterally, or of equivalent effective daily doses of active ingredient sublingually or transdermally, preferably 0.1-200 mg of active ingredient per day sublingually, and 0.1-100 mg of active ingredient per day transdermally.
A further aspect of the invention described herein is a process for producing (R)-carnitine on an industrial scale starting from the corresponding (S) enantiomorph, which is a raw material available in large amounts and at low cost, in that it is easily obtainable as a by-product of industrial processes of resolution of the racemic mixture of (R,S)-carnitine or (R,S)-carnitinamide with optically active acids such as tartaric acid, tartaric dibenzoyl acid, camphoric acid or camphorsulphonic acid, by means of the formation of derivatives of general formula (I) or (II).
A number of processes have recently been described for the production of (R)-carnitine starting from the corresponding (S) enantiomer; in particular, in U.S. Pat. Nos. 5,412,113 and 5,599,978 (S) carnitine is esterified to protect the carboxylic group; the ester thus obtained is then converted to the corresponding mesylate and subsequently subjected to hydrolysis to restore the carboxylic group; at a suitable pH value, a chiral lactone is formed which presents the desired (R) configuration which then yields (R)-carnitine by basic hydrolysis. This process, however, is not free of drawbacks, owing both to the fact that one has to protect and then deprotect the carboxylic function and because for formation of the mesylate to take place with good yields an excess of methane sulphonic anhydride has to be used with consequent formation of large amounts of methane sulphonic acid as a by-product, as well as because the formation of fairly large amounts of crotonoylbetaine as a by-product is possible.
In contrast, the process according to the present invention, which uses formula (I) derivatives, and preferably the one with Yxe2x95x90OH and Xxe2x88x92xe2x95x90NO3xe2x88x92, of absolute configuration (S), or the formula (II) compound of absolute configuration (S), easily obtainable starting from (S)-carnitine by treatment with acid nitrating mixtures, makes it possible to obtain (R)-carnitine, in a very simple manner, with a lower number of steps, a high yield and high stereospecificity, by treatment with inorganic and organic bases of the aforementioned formula (I) or (II) products in water or in mixtures of water and organic solvent mixable in water, operating at a pH value ranging from 7 to 10, and preferably at a pH value ranging from 7.5 to 9.5 and even more preferably from 8 to 9 and at a temperature of 50-100xc2x0 C. and preferably at a temperature of 60-80xc2x0 C. This process may occur even without isolation of the (I) or (II) derivatives and thus allow xe2x80x9cone potxe2x80x9d transformation of (S)-carnitine to (R)-carnitine. The preferred bases are bicarbonates of alkaline or alkaline-earth metals and potassium phthalimide.
Though of less industrial interest at this time, the inverse process for transforming (R)-carnitine into (S)-carnitine is obviously feasible with the same process.
A further aspect of the invention described herein is the process for preparing (R)-carnitine from (S)-carnitine or vice versa through the use of the formula (IV) intermediate enantiomerically enriched of absolute configuration (R) and (S), respectively, prepared in any way and preferably starting from a formula (I) derivative with Yxe2x95x90OR or NR1R2 with Rxe2x95x90H, C1-C10 alkyl, or substituted alkyl and where R1R2, equal or different from one another, are alkyl, hydrogen R1R2 and Xxe2x88x92xe2x95x90NO3xe2x88x92 by treatment with organic or inorganic bases in water or in mixtures of water and organic solvent mixable with water. 